Boffer panels have always been popular at any anime convention you attend (for those who don't know, it's basically gladiator play-fighting with harmless foam weapons). What if there were a fixed area dedicated to it all convention long- like the manga library, or the photo booth? Participants could come and go without having to carve it out on their schedule like a panel, and the spontaneity of just popping in to have a spar feels like it would be really fun. Imagine the hijinks cospayers could get into: Spontanious grudge match! Sephiroth vs Vash the stampede: GO!
It wouldn't take much; just a dedicated room/area, a couple of foam weapons for con-goers to use and maybe a staff member to supervise.